The Adephaga is two groups with a common origin. They are the Hydradephaga (water beetles) and the Geadephaga (ground beetles. They are mostly predatory. The first fossils of both groups are found in the Triassic period.[1] The ground beetles have formidable chemical defences. They have special pygidial glands which squirt out hot, burning chemicals. Bombardier beetles are famous for squirting their nasty chemicals at attackers.